Describe the structure of DNA

The structure of DNA

• A DNA molecule is composed of two antiparallel polynucleotide chains as shown above.
• Each chain consists of repeated units of deoxyribonucleotides formed by a deoxyribose sugar phosphate backbone with nitrogenous bases as side branches.
• The two polynucleotide chains are twisted around a common axis to form a right handed double helix.
• These two chains are held together by hydrogen bonds between the nitrogenous bases from either chain. Adenine in one chain is always pairs with thymine of the other by two hydrogen bonds while cytosine pairs with Guanine by three hydrogen bonds.
• The arrangement of these nitrogen bases gives DNA its identity.
• DNA in eukaryotes is wound around histone proteins to form chromosomes.
• In prokaryotes, it occurs in a circular shape.

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